Thermionic emissive cathode



Feb. 13, 1968 DOMOTOR 3,369,145

THERMIONIC EMISSIVE CATHODE Filed April 9, 1965 T'lc i- INVE TORATTORNEYS United States Patent 3,369,145 THERMIONIC EMISSIVE CATHODELorant Domotor, Newark, N.J., assignor to Wagner Electric Corporation, acorporation of Delaware Filed Apr. 9, 1965, Ser. No. 446,895 Claims.(Cl. 313346) ABSTRACT OF THE DISCLOSURE A thermionic emissive cathodefor use in electron discharge devices employs the oxides of barium,strontium, and lithium, resulting in a cathode which starts electronemission at a lower temperature than barium oxide or strontium oxide.

This invention relates to a thermionic emissive cathode for use inelectron discharge devices. The cathodes may be used with high vacuumtubes or gas filled tubes such as thyratrons. The invention hasparticular reference to an emissive coating composition including amixture of oxides which produce electrons rapidly and efliciently.

The use of barium and strontium oxides is Well known and cathodecoatings using these substances have been in use for many years. Themixtures are desopisted by spraying onto the base in the form ofcarbonates but during the processing of the discharge devive, thecarbonates are changed to oxides before the device is sealed. One of theobjections to this coating is the inability of the cathode to heat upquickly and assume an emissive temperature in less than about tenseconds. There are many devices and circuits in use today which requirea faster action. This is particularly true of television sets which,because of this delayed action, sometimes take thirty seconds beforeshowing a picture.

The present invention eliminates a considerable portion of this waitingtime and produces electron emission within a few seconds of the timewhen current is applied to the heater. This increased action is dueentirely to the addition of a small percentage of lithium carbon-ate tothe original mixture. After the processing of heating and evacuating,the carbonate changes to the oxide.

One of the objects of this invention is to provide an improvedthermionic emissive cathode coating which avoids one or more of thedisadvatages and limitations of prior art coatings.

Another object of the invention is to lower the time interval betweenthe application of current to the heater coil and the emission ofelectrons from the emissive surface.

Another object of the invention is to provide a cathode coating whichstarts its emissive action at a lower temperature than prior artcoatings.

The invention comprises a conductive metallic base "ice d-rical cathodehaving the emissive coating on the outside surfoce of the cylinder.

FIG. 2 is a cross sectional view of the cathode shown in FIG. 1 and istaken along line 2-2 of that figure.

FIG. 3 is a cross sectional view of a gaseous discharge device having ananode, a firing electrode, and a cathode with its emissive coating onthe inside surface of a hollow cylinder.

Referring now to the drawings, the cathode shown in FIGS. 1 and 2includes a hollowcylinder 10 having a heater wire 11 disposed inside thehollow portion. On the outside surface of the cylinder an emissivecoating 12 is deposited, generally by spraying. When the tube is firstassembled, the emissive coating contain-s about parts of bariumcarbonate, 57 parts of strontium carbonate and about 3 parts of lithiumcarbonate. While these pro portions are considered to be the preferredproportions, small variations (:5 parts of the barium carbonate, :5parts of the strontium carbonate, :1 part of the lithium carbonate) arepermissible and therefore the invention is not limited to the exactproportions listed above. After the parts assembled within an envelope,the air is pumped out and the temperature of the cathode is raised to anemissive temperature. This action changese all the carbonates to oxides,giving off carbon dioxide which is pumped out of the envelope by thevacuum pumps.

The device shown in :FIG. 3 is a thyrat-ron having an envelope 13 and ananode 14 surrounded by a shield 15. The anode is supported by a rod 16which is sealed to the envelope and forms a lead-in conductor. Thebottom portion of shield 15 contains cut out portions 17 which act as afiring electrode and pass the current between anode and cathode when thetube is conductive. Below the shield 15 is a cathode 18 including ametallic supporting cylinder 20 and an emissive coating 21 on its insidesurface. A coil of heating wire 22 is disposed adjacent to the outsidesurface of cylinder 20 for heating the cylinder and its coating to anemissive temperature. The outside portion of the heater wire 22 may becovered by another cylinder 23'to conserve heat and keep the temperatureof the envelope at a lower range. The usual lead-in conductors 24 forthe shield, 25 for the heater wires, and 26 for the cathode are sealedin the envelope in conventional manner.

When the heater wire 11 (or 22) receives its normal value of current,the temperature of the base and the portion which may be a hollowcylinder. A heater wire is positioned within the cylinder (or outside ofit) for heating it to an emissive temperature. An electron emissivecoating is deposited on the outside (or inside) surface of the cylinder,this coating including by weight about 50 parts of barium carbonte,about 47 parts of strontium carbonate and about 3 parts of lithiumcarbonate. When a cathode is used for heavy duty gaseous dischargedevices, the emissive coating may be deposited on the inside surface ofthe cylinder with the heater wire disposed adjacent to the outsidesurface.

For a better understanding of the present invention, together with otherand further objects thereof, reference is made to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 is a side view, with parts cut away, of a cylincoating both heatup in a manner similar to prior art cathodes. However, the lithium oxidestarts its electron emission at a much lower temperature than the bariumand strontium mixture, cutting down the starting time to about one halfthe usual time interval. After the cathode has reached its normaltemperature, the barium and strontium oxides provide the emissiveaction.

The foregoing disclosure and drawings are merely illustrative of theprinciples of this invention and are not to be interpreted in a limitingsense. The only limitations are to be determined from the scope of theappended claims.

I claim:

1. A thermionic emissive electrode comprising a conductive metallichollow member, an electron emissive coating on one surface of the memberand a heater for the member for heating it to an emissive temperature,said coating comprising by weight 45 to 55 parts of barium oxide, 42 to52 parts of strontium oxide and 2 to 4 parts of lithium oxide.

2. A thermionic emissive electrode comprising a conductive metallichollow member, a heater within the member for heating it to an emissivetemperature and an electron emissive coating on the outer surface of themember, said coating prior to heating and exhaust operations comprisingby weight 45-55 parts of barium carbonate, 42-52 parts of strontiumcarbonate and 2 to 4 parts of lithium carbonate.

3. A thermionic emissive electrode comprising a conductive metallichollow member, a heater disposed on the outside of the member forheating it to an emissive temperature, and an electron emissive coatingon the inner surface of the member, said coating prior to heating andexhaust operations comprising by Weight 45 to 55 parts of bariumcarbonate, 42 to 52 parts of strontium carbonate, and 2 to 4 parts oflithium carbonate.

4. A thermionic emissive electrode within an electron discharge deviceafter heating and exhaust operations comprising a conductive metallichollow member forming a cathode, a heater within the member for heatingit to an emissive temperature, and an electron emissive coating on theouter surface of the member, said coating comprising by weight 45 to 55parts of barium oxide, 42 to 52 parts of strontium oxide, and 2 to 4parts of lithium oxide.

5. A gaseous discharge device comprising an envelope, an anode, a firingelectrode, and a cathode Within the envelope, said cathode including aconductive metallic References Cited UNITED STATES PATENTS 2,473,3586/1949 Bright 313345 X 2,840,751 6/1958 Meister et al 313346 X 2,986,6715/1961 Kersetter et a1. 313-845 X 3,147,362 9/1964 Ramsey et al. 313-346X FOREIGN PATENTS 1,310,430 10/1962 France.

JOHN W. HUCKERT, Primary Examiner.

A. 1. JAMES, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,369,145 February 13, 1968 Lorant Domotor It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 26, for "desopisted" read deposited line 28, for "devive"read device line 46, for "disadvatages" read disadvantages line 62, for"carbonte" read carbonate column 2, line 15, for "57" read 47 line 22,after "parts" insert are line 24, for "changese" read changes column 4,line 3, for "emisive" read emissive Signed and sealed this 29th day ofApril 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J BRENNER Attesting Officer Commissionerof Patents

